Pressostat

ABSTRACT

The invention is a pressostat assembly which includes two bellows, one inside the other, which have fluid communication. Both bellows are fixedly attached to a rod form of operating member and the outer bellows operates to impart a closing movement to the operating member if the inner bellows should develop a leak. The effective cross sectional area of the outer bellows is larger that that of the inner bellows.

United States Paten Kraemer Oct. 23, 1973 [54] PRESSOSTAT 2,342,5792/l944 Hagemann 92/35 X 2,663,155 12/1953 Strobell 92/35 x [751 Invenm"Kramer Nordborg 2,761,927 9 1956 Szypulski 200/83 c Denmark 2,795,2396/1957 Eckman et a1. 92/37 x 2,988,282 6/1961 HOlIlenfOth 92 35 x [73]Ass'gnee' Danfoss Nordborg Dermark 3,055,219 9/1962 Wilson et a1 73 41022 Filed: May 24, 1972 Appl. No.: 256,565

Foreign Application Priority Data May 25, 1971 Germany P 21 25 809.3

US. Cl 92/35, 73/389, 73/410,

. 92/37, 200/83 C Int. Cl. F0111 19/00, F16j 3/00 Field of Search 92/35,37, 39, 43'

References Cited UNITED STATES PATENTS 10/1942 Carter et al 92/35 XPrimary Examiner-Martin P. Schwadron Assistant Examiner-Abe HershkovitzAttorney-Wayne B. Easton [57] ABSTRACT The invention is a pressostatassembly which includes two bellows, one inside the other, which havefluid communication. Both bellows are fixedly attached to a rod form ofoperating member and the outer bellows operates to impart a closingmovement to the operating member if the inner bellows should develop aleak. The effective cross sectional area of the outer bellows is largerthat that of the inner bellows.

4 Claims, 1 Drawing Figure PRESSOSTAT The invention relates to apressostat comprising an operating element, bounded by an operatingbellows or the like and connected to an installation, a spring acting inthe opposite direction to that of the pressure in the operating element,and a switching member which is actuated when a pressure limit isexceeded in the operating element, the pressostat being intended for useparticularly in refrigerating installations.

A pressostat of this kind is intended to actuate the switching member assoon as the pressure limit in the operating element is reached. In thecase of a high pressure pressostat for a refrigerating installation, thecurrent to the compressor motor is switched off for example when thepressure in the installation has reached a predetermined level above thenormal operating pressure, as a result, for instance, of the failure ofthe air circulating system or of the supply of cooling water. Suchpressostats are suitable as safety switches in other installations inwhich a medium is caused to move under pressure.

The quality of pressostats of this kind is required to be very high,since leaking of the operating element, whether due to a fracture in theoperating bellows or the like or to damage to a soldered joint, willhazard the functional reliability of the equipment. Fine hair linecracks are particularly dangerous since these are not immediatelydetected. In a refrigerating installation, for example, refrigerantescapes from the installation over fairly lengthy periods of timewithout any other safety device in the installation responding to thisloss.

A thermostatic valve is known in which the operating element is boundedby an inner and outer bellows. The inner bellows operates in a directionopposite to that of the spring and serves to displace the closingmember. The outer bellows, under the action of the pressure that obtainsin the operating element, holds a support plate, acting as a backingelement for a safety spring, against a stop. When the pressure in theoperating element drops, e.g. because one of the operating bellowsbreaks, the safety spring acts on the closing member and closes thevalve.

Thermostatic valves are also known in which the operating element isconstituted by the annular chamber between two parallel operatingbellows so that a space through which a valve spindle can bepassedremains in the annular space.

The object of the present invention is to provide a pressostat of theinitially stated kind which not only operates in its normal manner butalso provides a switching action soon after any damage has occurred toit.

According to the invention, this object is achieved by fitting theoperating bellows in an enclosed protective chamber, part of the outerwall of which is formed by an additional bellows which likewise acts ina direction opposite to that of the spring and actuates the switchingmember when a pressure limit below that of the operating element isexceeded in the protective chamber.

In the case of a pressostat of this kind, a predetermined pressure,which has no effect upon the normal operation of the pressostat,normally obtains in the protective chamber. However, if the operatingelement or the like begins to leak, the pressure obtaining in theoperating element is set up in the protective chamber. By means of anappropriate design of the additional bellows, the switching member canthen be actuated even at a lower pressure. In particular, this pressurelimit in the protective chamber can be below the normal pressure rangeof the pressostat. This means that leakage of the operating elementleads to response of the switching member even during normal operation,so that the installation is switched off soon after the leak hasdeveloped.

In a preferred construction, the additional bellows surrounds theoperating bellows, has a greater effective pressure surface thanthe'latter, and is connected to the output-adjusting member of theoperating element. The greater effective pressure surface results in alower pressure in the protective chamber being sufficient to produce aforce which overcomes the force of the spring exerting counter-pressure.Furthermore, the system composed of the spring, the switching member andthe output-adjusting member can be the same as that used in a simplepressostat.

There are other possible ways of setting the required pressure limit inthe protective chamber to a low level. For example, this can be achievedif the operating bellows and the additional bellows each engage a leverby means of an output adjusting member, but at different distances fromthe pivot point, and if the lever is biased by the spring in theopposite direction and is used to actuate the switching member.

Particular advantage accrues if, in addition, the pressure in thesealed-off protective chamber is below atmospheric pressure. In this waythe additional bellows is self-monitoring. Thus, if a leak develops dueto breakage of the additional bellows or of an associated solderedjoint, atmospheric pressure is set up in the protective chamber. Thispressure suffices to actuate the switching member.

A particularly simple construction is obtained if the output-adjustingmember simply bears in a mechanically positive manner against theoperating bellows. The two systems can then be simply fitted one withinthe other and soldered up. Nevertheless, a specific mode of operation isachieved in all operating conditions. Furthermore, changes in pressurein the protective chamber can occur without being impeded by theoperating bellows.

The invention will now be described in greater detail by reference to anembodiment illustrated in the drawing which shows diagrammatically andin section a pressostat in accordance with the invention.

By means of the port 5, a bush 3 of a pressostat 4 is inserted into awall 1 of a container 2 of an installation in which refrigerantcirculates, and the bush is held in position by means of a nut 6. Theport contains a con- 'of the bush 3, a bellows 10 having a pressuresurface 11, the base 12 of the bush 3, and a ring 13 which is connectedto the operating bellows 10 and is soldered to the wall 9. Anoutput-adjusting member 14 in the form of a stem acts on a lever 15which is adapted to swing about a pivot point 16. The lever is biased bya rated-value spring 17 which is supported by a preferably adjustablebacking element 18. The free end of the lever 15 actuates a switchingmember 19 which is here the plunger 20 of a micro-switch.

The operating element 8 is-surrounded by a protective chamber 21 whichis bounded by an additional bellows 22 having a pressure surface 23, theside-wall 9 of the bush 3 and a flange 24 on this bush. The additionalbellows 22 is soldered at 25 to the flange 24 and at 26 3 to theoutput-adjusting member 14. The pressure surface 23 is a multiple of thepressure surface 11. During normal operation of the system the pressurein the sealed-off protective chamber 21 is below that of the atmosphere.

The pressostat 4 operates in the following manner. If the pressure 'inthe container 2 of the installation rises, the same pressure is set upin the operating element 8. If this pressure exceeds a predeterminedlevel which is a certain amount above the normal operating levels, theoperating bellows 10 displaces the output-adjusting member 14 therebyovercoming the force of the spring 17. This causes the lever 15 to swingin the counterclockwise direction and the microswitch 19 to be actuated.This can be utilized for switching off the circulating system of theinstallationeg. of a refrigerating machine.

If the operating bellows 10 should break, the same pressure as that inthe operating element 8 is set up in the protective chamber 21 after ashort time. As a result of the large pressure surface 23, a considerablylower pressure than that used in normal operation suffices to overcomethe force of the rated-value spring 17 and to actuate the microswitch19. Development of a leak in the operating element 8 therefore leads tothe rated-value spring 17, and the microswitch 19 is actuated.

Thus the pressostat is not only a safety member which monitors anyexcessive rise in pressure in the installation, but it also preventsunintentional escape of the pressurized medium from the installation,and switches it off shortly after the occurrence of a leak in theoperating element. Furthermore, those parts used for this additionalfunction are designed to be selfmonitoring.

I claim:

1. A pressostat assembly comprising a casing forming a chamber having afluid inlet and a fluid pressure equalizing port, a first bellows insaid chamber and attached to said casing, said first bellows having anopen end in surrounding relation to said port, a rod inside said firstbellows attached to the opposite end thereof and extending through saidport, a second bellows attached to and surrounding said casing, saidsecond bellows having one end thereof attached to said rod in fluidtight relation thereto.

sectional area than said first bellows.

4. A pressostat assembly according to claim 1 wherein the gaseouspressure internally of said first be]- lows is lower than atmosphericpressure.

1. A pressostat assembly comprising a casing forming a chamber having afluid inlet and a fluid pressure equalizing port, a first bellows insaid chamber and attached to said casing, said first bellows having anopen end in surrounding relation to said port, a rod inside said firstbellows attached to the opposite end thereof and extending through saidport, a second bellows attached to and surrounding said casing, saidsecond bellows having one end thereof attached to said rod in fluidtight relation thereto.
 2. A pressostat assembly according to claim 1including spring means biasing said rod in the direction of saidopposite end.
 3. A pressostat assembly according to claim 1 wherein saidsecond bellows has a larger effective cross sectional area than saidfirst bellows.
 4. A pressostat assembly according to claim 1 wherein thegaseous pressure internally of said first bellows is lower thanatmospheric pressure.